Sorry for all the questions but just read there too there will be speed improvements in the Pro version will that really make a difference from a Internal SATA 4 TB drive to a External 4 TB IDE/SATA drive ?

Real-time backups run as soon as (and only if) there are any changes at the source. They can be paced using "minimum pause between backups" option so that they don't run more often than every N time units.

Scheduled backups are run at set intervals, including cases when there were no changes to the source. Bvckup 2 will understand that once it scans the source, but it still needs to scan the source first.

Another thing to consider is that there is a fixed cost to running every backup including the time needed to create a volume snapshot (if using shadow copying) and the time needed to scan source/destination. So the decision to use real-time or scheduled option would also depend on how quick these steps are in your setup.

Thinking of upgrading to Pro

We are still on an older licensing scheme with Personal and Pro licenses that don't differ functionally, only in permitted usage scenarios. The licensing change has been slow coming and it's still at least a month away, likely more.

Speed improvements in Internal => External case

Parallel copying won't lead to any notable speed up if either drive is HDD. Conversely, if they were both SSD/NVMe, then - yes, parallel copying within the same system is likely to help with speeding up the transfer.

I am still not sure if I should do Real-time backups or Scheduled backups.

I will give you some examples of what my system does. For example I download a lot of linux isos from newsgroups and my speed is only 50 Mbps about. So it takes around 10 minutes sometimes 1 hour, if connection is being used in the house a lot by streaming services because I have my router set to slow down all other traffic especially newsgroups so it doesn't effect streaming making it buffer.

Plus ever night at 3:30 am a Macrium Reflect incremental image is created of my whole system which normally takes less than 10 minutes.